This invention relates to a process for forming a coating and an organic coating.
The invention is particularly concerned with at least two different coatings on metallic surfaces and preferably on aluminum, copper, iron, magnesium, zinc or of an alloy containing aluminum, copper, iron, magnesium and/or zinc.
The term xe2x80x9cconversion coatingxe2x80x9d is a well known term of the art and refers to the replacement of native oxide on the surface of a metallic material by the controlled chemical formation of a film on the metallic surface by reaction with chemical elements of the metallic surface so that at least some of the cations dissolved from the metallic material are deposited in the conversion coating. Other coatings are formed on the surface of the metallic material without or without significant deposition of constituents dissolved by chemical reactions with the metallic material.
In the search for alternative, less toxic coatings than chromium containing coatings, research has been conducted on non-conversion coatings and on conversion coatings based e.g. on zirconium and/or titanium as well as fluoride containing aqueous solutions instead of chromium bearing solutions.
However, there is considerable room for improvement in the adhesion and corrosion protection properties of prior titanium/zirconium-fluoride based coatings. The need for improvement is particularly true for coatings on certain metal alloys, such as 1000, 2000, 3000, 5000 and 6000 series aluminum alloys, which coatings can have variable adherence or no adherence.
Over the years there have been numerous attempts for the replacement of chromating chemicals by ones less hazardous to the health and the environment. Their major disadvantage is that they either form coatings with poor paint adhesion properties or there are working concentrations required showing a risk of blue discoloration which does not disturb performance but makes the process undesirable in the eyes of the users. Zirconium and titanium based coating processes have found some applications in certain market niches, but they have failed in the past 25 years to replace chromating as a pretreatment prior to painting especially of aluminum, magnesium, zinc or their alloys.
Accordingly, it is an object of the present invention to provide a surface treatment process for the surface of a metallic material which overcomes, or at least alleviates, one or more of the disadvantages or deficiencies of the prior art. It is also an object of the present invention to provide an aqueous, titanium/zirconium-fluoride containing coating solution for use especially together with a further organic coating or paint. Specifically, it was an object of this invention to propose such a process to suit industrial requirements of short time formation of the coating and of near-ambient operating temperature.
It has been discovered that the combination treatment of a titanium/zirconium-fluoride treatment with an application of self assembling molecules can greatly promote corrosion resistance and paint adhesion of the coating.
According to the present invention, there is provided a process of treating metallic surfaces showing at least two separate steps for applying two different coatings one after the other, whereby the metallic surfaces are contacted at a temperature in the range of from 10 to 100xc2x0 C. first with an aqueous solution A and later on with an aqueous solution B or vice versa characterized in that the solution A contains an effective amount of zirconium, hafnium, titanium, silicon and/or boron as well as of fluoride in the form of ions and/or complex ions able to pickle the metallic surface and to generate a coating on the pickled metallic surface and that the solution B contains an effective amount of one or more compounds of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X*, where Y is an organic group with 2 to 50 carbon atoms, where X as well as Z is a groupxe2x80x94each same or differentxe2x80x94of OHxe2x80x94, SHxe2x80x94, NH2xe2x80x94, NHRxe2x80x2xe2x80x94, CNxe2x80x94, CHxe2x95x90CH2xe2x80x94, OCNxe2x80x94, CONHOHxe2x80x94 (=hydroxamic), COORxe2x80x2 (=alkyl ester), acrylamide-, epoxide-, CH2xe2x95x90CRxe2x80x3xe2x80x94COOxe2x80x94, COOHxe2x80x94, HSO3xe2x80x94, HSO4xe2x80x94, (OH)2POxe2x80x94, (OH)2PO2xe2x80x94, (OH)(ORxe2x80x2)POxe2x80x94, (OH)(ORxe2x80x2)PO2xe2x80x94, SiH3xe2x80x94, Si(OH)3xe2x80x94, where Rxe2x80x2 is an alkyl group with 1 to 4 carbon atoms, where Rxe2x80x3 is a hydrogen atom or an alkyl group with 1 to 4 carbon atoms, and where the groups X and Z are each bound to the group Y in their terminal position, where Y* is an organic group with 1 to 30 carbon atoms, where X* as well as Z* is a groupxe2x80x94each same or differentxe2x80x94of OHxe2x80x94, SHxe2x80x94, NH2xe2x80x94, NHRxe2x80x2xe2x80x94, CNxe2x80x94, CHxe2x95x90CH2xe2x80x94, OCNxe2x80x94, CONHOHxe2x80x94 (=hydroxamic), COORxe2x80x2 (=alkyl ester), acrylamide-, epoxide-, CH2xe2x95x90CRxe2x80x3xe2x80x94COOxe2x80x94, COOHxe2x80x94, HSO3xe2x80x94, HSO4xe2x80x94, (OH)2POxe2x80x94, (OH)2PO2xe2x80x94, (OH)(ORxe2x80x2)POxe2x80x94, (OH)(ORxe2x80x2)PO2xe2x80x94, SiH3xe2x80x94, Si(OH)3xe2x80x94,  greater than Nxe2x80x94CH2xe2x80x94PO(OH)2xe2x80x94, xe2x80x94Nxe2x80x94[CH2xe2x80x94PO(OH)2]2-where Rxe2x80x2 is an alkyl group with 1 to 4 carbon atoms, where Rxe2x80x3 is a hydrogen atom or an alkyl group with 1 to 4 carbon atoms.
The process according to the invention may be characterized in that the metallic surfaces consist essentially e.g. of aluminum, copper, iron, magnesium, zinc or of an alloy containing aluminum, copper, iron, magnesium and/or zinc. p In the following it is not distinguished between the metallic surfaces and the already coated metallic surfaces, especially, if both possibilities may be possible at the same time, e.g. with reaction products and deposited compounds of the solution A not to make the text too complicate as the expert in the art knows what is meant. Furtheron, it is not distinguished by this term, if there is a very thin xe2x80x9cnaturalxe2x80x9d oxide and/or hydroxide layer. This oxide and/or hydroxide layer is typically extremely thin, mostly of few nm thickness. The solution A according to the invention may react chemically with the metallic surface by depositing cations in the coating being dissolved from the metallic material, but must not. Therefore, the coating is not generally called a conversion coating, although this may be in some cases a conversion coating.
Further on, it is preferred to have in the solution A concerning the fluoride content of the solution a high or very high percentage of complex fluoride and no or a low percentage of fluoride ions. In the case that in the same solution A titanium and zirconium would be present, it is preferred that the content of titanium is higher than the content of zirconium. On the other hand, it may be often preferred to have a content mainly or only of zirconium referring to chemical elements selected from the group of titanium, zirconium, hafnium, silicon and boron. Normally, no further additive is necessary for the use of solution A; in the case that a further additive is necessary, then surfactants, acids, or alkaline materials may be added. The coating formed by contacting the metallic surface may be a conversion or may be a non-conversion coating, depending on the type of metallic surface and on the contacting conditions. This coating is favorably located directly on the very thin oxide/hydroxide layer formed on the metallic surface or even directly on the metallic surface and contains often titanium, zirconium, hafnium, silicon and/or boron as well as hexafluoride and/or oxide/hydroxide. In the process according to the invention, the compounds of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X* used in the solution B may preferably show a group Y with 3 to 30 carbon atoms, more preferred with 4 to 20 carbon atoms, much more preferred with 4 to 16 carbon atoms, especially preferred with 9 to 14 carbon atoms as well as a group Y* with 2 to 24 carbon atoms, more preferred with 3 to 20 carbon atoms, much more preferred with 4 to 16 carbon atoms, especially preferred with 9 to 14 carbon atoms. It is preferred that the groups X* and Z* of the compounds of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X* are each bound to the group Y* in their terminal positions. In preferred embodiments, the compounds of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X* are able to form self assembling molecules which may form a layer, especially a thin layer or even a monolayer, of these self assembling molecules (SAM) on the metallic surfaces.
These compounds may show a group Y or Y* that is a linear unbranched group. Alternatively, these groups Y or Y* may be a linear group branched with at least one functional group, preferably branched with at least one alkyl group and/or one aromatic group. The functional groups may stand aside from the linear group.
The most effective constituent of the solution B may be a compound XYZ, X*Y*Z* and/or X*Y*Z*Y*X* with a group Y or Y* that has an even number of carbon atoms. Besides this most effective constituent which may have self assembling molecules there may be any surfactant in the solution B to improve the rate of deposition of self assembling molecules. Often compounds are used according to the process of the invention which may be able to form self assembling molecules and which may organize themselves parallel one to the other and in about perpendicular to the metallic surfaces with the hydrophobic regions of the molecules located at the metallic surfaces and with the hydrophilic regions of the molecules extending into the liquid away from the metallic surfaces. Nevertheless, there is no necessity that these compounds organize their molecules in such a way to generate coatings. There is the target to form a uniform coating quality as far as possible and an at least randomly distribution of islands of molecules of the solution B, but not the necessity of totally covering the metallic surfaces. Often even a very short exposure of the solution B to a metallic surface may lead to a random distribution of at least one of the compounds of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X*, nevertheless, sometimes a longer contacting time may be preferable for a high surface quality.
For the process according to the invention it is preferred that at least one compound of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X* is present in the aqueous solution as salt and/or acid.
The more effective constituents of the solution B may be compounds XYZ, X*Y*Z* and/or X*Y*Z*Y*X* with an unbranched straight-chain alkyl group with 3 to 30 carbon atoms as Y or Y*. Preferably, this group Y or Y* has 4 to 20 carbon atoms, more preferred 4 to 18 carbon atoms, much more preferred 5 to 14 carbon atoms and most preferred 10 to 14 carbon atoms.
In specific embodiments, the compound XYZ, X*Y*Z* and/or X*Y*Z*Y*X* may have as Y or Y* an unbranched straight-chain group consisting of 1 to 4 aromatic C6H4 nuclei connected in the para-position, or a group consisting of 1 or 2 unbranched, straight-chain alkyl residues each with 1 to 12 carbon atoms or 1 to 4 aromatic C6H4 nuclei connected in the para-position.
The most effective constituent of the solution B may be a compound XYZ, X*Y*Z* and/or X*Y*Z*Y*X* with a group Y or Y* that is an unbranched, straight-chain alkyl group with 6 to 14 carbon atoms or a p-CH2xe2x80x94C6H4xe2x80x94CH2-group or a p,pxe2x80x2-C6H4xe2x80x94C6H4-group.
The most effective constituent of the solution B may be a compound XYZ, X*Y*Z* and/or X*Y*Z*Y*X* with a group (OH)2PO2xe2x80x94 or (OH)(ORxe2x80x2)PO2xe2x80x94 as X or X*. The most effective constituent of the solution B may be a compound XYZ, X*Y*Z* and/or X*Y*Z*Y*X* with a group (OH)2PO2xe2x80x94, (OH)(ORxe2x80x2)PO2xe2x80x94, OHxe2x80x94, SHxe2x80x94, NHRxe2x80x2xe2x80x94, CHxe2x95x90CH2 or CH2xe2x95x90CRxe2x80x3xe2x80x94COOxe2x80x94 as Z or Z*.
In preferred embodiments, the aqueous solution may contain at least one compound of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X* selected from the group of:
1-phosphonic acid-12-mercaptododecane,
1-phosphonic acid-12-(N-ethylamino)dodecane,
1 -phosphonic acid-12-dodecene,
p-xylylene diphosphonic acid,
1,10-decanediphosphonic acid,
1,12-dodecanediphosphonic acid,
1,14-tetradecanediphosphonic acid,
1-phosphoric acid-12-hydroxydodecane,
1-phosphoric acid-12-(N-ethylamino)dodecane,
1-phosphoric acid-12-dodecene,
1 -phosphoric acid-12-mercaptododecane,
1,10-decanediphosphoric acid,
1,12-dodecanediphosphoric acid,
1,14-tetradecanediphosphoric acid,
p,pxe2x80x2-biphenyldiphosphoric acid,
1-phosphoric acid-12-acryloyldodecane,
1,8-octanediphosphonic acid,
1,6-hexanediphosphonic acid,
1,4-butanediphosphonic acid,
1,8-octanediphosphoric acid,
1,6-hexanediphosphoric acid,
1,4-butanediphosphoric acid,
aminetrimethyleneposphonic acid,
ethylenediaminetetramethylenephosphonic acid,
hexamethylenediaminetetramethylenephosphonic acid,
diethylenetriaminepentamethylenephosphonic acid and
2-phosphonobutane-1,2,4-tricarboxylic acid.
In the process according to the invention the time of contacting the metallic surfaces with the solution. A may be in the range of from 0.001 seconds to 10 minutes. Applications in the coil industry may need contacting times in the range of from 0.001 seconds to 30 seconds, whereas other applications may often necessitate contacting times in the range of from 1 minute to 3 minutes. For the contacting of wheels, a time range of from 10 seconds to 5 minutes are preferred and of from 30 seconds to 2 minutes are more preferred. For the coil coating process, a contacting time range of from 0.002 to 20 seconds is preferred, of from 0.01 to 8 seconds is more preferred. For the contacting of singular metallic parts, a time range of from 10 seconds to 10 minutes is often preferred and of from 20 seconds to 6 minutes is more preferred. If the contacting time is very short, the percentage of the metallic surface being covered with at least one of the compounds of the type XYZ, X*Y*Z* and X*Y*Z*Y*X* may be relatively low and/or the molecules of these compounds may be not or only partially assembled. The longer the contacting time, the higher may be the percentage of metallic surface covered with at least one of these compounds. The longer the contacting time, the higher may be the percentage of molecules that are arranged perpendicular to the metallic surface as a reason of the self assembling effect. Although compounds of the type XYZ, X*Y*Z* and X*Y*Z*Y*X* with Y or Y* having 10 to 14 carbon atoms gave excellent results of corrosion inhibition and paint adhesion, it has been found that even in the cases that these compounds should not form a continuous coating on the metallic surface, but only a smaller or higher percentage of coating islands distributed on the metallic surface and/or that these compounds did not or only partially arrange perpendicular to the metallic surface, the such prepared coatings were astonishingly good concerning paint adhesion and corrosion inhibition.
The aqueous solution A may have a pH value in the range of from 1 to 5, preferably in the range of from of 2 to 4 and more preferred in the range of from 2.5 to 3.5 if the concentration of fluoride anions is in the range of from 10 to 1000 mg/L, but the pH value is preferably in the range of from 1 to 3 if the concentration of fluoride anions is in the range of from 6,000 to 18,000 mg/L. At a lower pH value than 1, a suitable coating according to the invention will be generated, but normally significantly higher pH values will be used. At a pH value higher than 5, an instability of the solution A may occur in some cases; but if this instability does not occur due to the specific conditions, an acceptable coating will be created. The pH value may be adjusted within the regular coating process to values of e.g. 4.0 or 4.2 minimum, preferably by adding a fluoride containing compound, which may be in a water soluble form, to cut the pH value down to e.g. 4.2. The buffering of the solution A may be made favorably by any addition, e.g. of sodium fluoride or ammonium bifluoride.
The solution A may preferably be applied to the metallic surface at a temperature of up to 30xc2x0 C. to avoid in every case blue discoloration of the coating. The solution B may preferably be applied to the metallic surface at a temperature of up to 60xc2x0 C. The process according to the invention may be characterized in that in the solution A the concentration of the titanium is in the range of from 0.0001 to 0.1% by weight if titanium is added, the concentration of the zirconium is in the range of from 0.0001 to 0.1% by weight if zirconium is added, the concentration of the hafnium is in the range of from 0.0001 to 0.1% by weight as hafnium added intentionally, whereby only one selected from the group of titanium, zirconium, hafnium, silicon and boron has to be present. Instead of or together with at least one of the chemical elements of the group of titanium, zirconium and hafnium, silicon and/or boron may be used. The total amount of all the five chemical elements present in the solution may be in the range of from 0.0001 to 0.2% by weight. Preferably, the concentration of titanium, zirconium, hafnium, silicon and/or boron each may be in the range of from 0.0008 to 0.05% by weight, more preferred in the range of from 0.001 to 0.02% by weight. A mixture of at least two of them may be favorable to generate a combination effect with improved results, especially of the combination of titanium with zirconium. Furtheron, it is more preferred that the range of the concentration when used for spraying is of from 0.002 to 0.08% by weight of titanium, zirconium, hafnium, silicon and/or boron each, much more preferred of from 0.005 to 0.025% by weight. The solution A may contain ZrOCl2 which may be very advantageous.
The concentration of the total fluoride may be in the range of from 0.001 to 0.2% by weight calculated as fluoride. The concentration of the total fluoride in the solution A may be preferably in the range of from 0.005 to 0.15% by weight, more preferred in the range of from 0.01 to 2% by weight, much more preferred of from 0.008 to 0.09% by weight. The moiety of complex fluoride anions at the total of the fluoride may be in the range of from 50 to 95%. If there is less titanium, zirconium, hafnium, silicon and/or boron in the solution A, then there will be less fluoride necessary; an excess of fluoride with regard to the content of titanium, zirconium, hafnium, silicon and/or boron enhances the pickling effect and may help to control the thickness of the generated coating. If there is a too high content of titanium, zirconium, hafnium, silicon and/or boron in the solution A in relation to the total fluoride content, then there will be a thicker coating which may disturb in some cases when a paint will be later applied upon as such a too thick coating may lead to filiform corrosion and a worse paint adhesion; furtheron, there may occur only a very weak pickling effect.
The aqueous solution A shows primarily a pickling effect, but even some deoxidation effect. Then a reaction to generating a coating may occur, which may for example contain hydroxides, oxides and other compounds of aluminum and/or other metallic elements that are constituents of the metallic material together with titanium, zirconium, hafnium, silicon and/or boron.
The coating containing titanium, zirconium, hafnium, silicon and/or boron may show a thickness in the range of from 0.1 to 100 nm. Its coating weight may be in the range of from 1 to 100 mg/m2.
The coating containing one or more compounds of the type XYZ, X*Y*Z* arid/or X*Y*Z*Y*X* may show a thickness which is measured in the range of from 0.1 to 100 nm, often in the range of from 1 to 20 nm. Its coating weight may be often in the range of from 1 to 20 mg/m2, but it may be even higher than 20 mg/m2 or sometimes even in the range of about 80 or 120 mg/cm2 as for cans and other containers. If the concentration of the solution B is significantly enlarged, the thickness of the generated coating often may remain in the same thickness range as applied with a much more diluted solution B.
The concentration of the solution B may vary in the range of from 0.00001 to about 50%, whereby the upper concentration limit is greatly dependent on the water solubility limit of the used compounds and the specific conditions. If compounds are used with relative short chain length of Y resp. Y* then the water solubility may be much enhanced. If the chain length of Y resp. Y* is in the range of from 10 to 14 carbon atoms, then the water solubility is reduced significantly and there may be a solubility limit of about 1%. This effect is proportional to the chain length and hydrophobicity of the hydrocarbon chain: The longer the hydrocarbon chain, the higher the hydrophobicity properties. Furtheron, the higher the concentration of these compounds in solution B, the greater may be the possibility to generate foam which is undesirable. For example, the dodecanediphosphonic acid may be dissolved in water without further aids in the range of from 100 to 300 mg/L, whereas it can be dissolved in hot water in an amount of up to 600 mg/L. For the amount of dodecanediphosphonic acid dissolved it may be an influencing factor, if the compound added is of low or of high purity. The amount of dissolved dodecanediphosphonic acid can be greatly enhanced by adding organic solvents. Such a proportion of an organic solvent may aid for quicker drying and may help to generate a higher concentration of the compounds of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X* in the solution B than without such organic solvent. Without any organic solvent, there are often only up to 400 mg/L of compounds of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X* in solution B, whereas with an organic solvent, its concentration can be enhanced up to a much higher extent.
It may be favorable, not to use any organic solvent. When an organic solvent is used, it may replace 0.01 to 50% of the water. This solvent may be an alcohol with 1 to 4 carbon atoms, acetone, dioxane and/or tetrahydrofurane.
It is preferred that the solution B contains essentially no further cations added intentionally. Furtheron, it is preferred that solution B contains essentially no nitrites, no nitrates and no peroxocompounds.
The water quality used for the preparation of solution B may be a water quality like natural water of very low hardness or like de-ionized water. The water quality shows preferably an electrical conductivity of less than 20 xcexcS/cm, but in some cases values of less than 200 xcexcS/cm may be sufficient.
Such a solution B containing only pure water and dodecanediphosphonic acid may show a pH value in the range of from 2.5 to 3.5. For the pretreatment of cans and other containers, a pH value in the range of from 0.5 to 2.5 may be preferred. Such a solution may show an electrical conductivity in the range of from 200 to 350 xcexcS/cm, if the pure water used had an electrical conductivity of less than 20 xcexcS/cm. The bath of the solution B may preferably be controlled with a photometer for the phosphorus and phosphate content or via measurement of the electrical conductivity. If the last mentioned method is used for controlling, the range of electrical conductivity may be held for dodecanediphosphonic acid in pure water in the range between 250 and 300 xcexcS/cm. The solution B can be controlled and maintained very easily in a well workable state.
The pH values of the solution B may vary in the range of from 1 to 10, preferably in the range of from 1.5 to 5.5, more preferred for some of the applied compounds in the range of from 1.8 to 4, whereas for others having alkaline additives the preferred range may be of from 7 to 14, preferably in the range of from 8 to 12, more preferred in the range of from 9 to 11. Most of the phosphorus containing compounds of the solution B may be used with such low pH values as mentioned above first, but some may be used with a higher pH value. As further additives to solution B may be used e.g. any alcohol, any silane, any amine, any phosphate, any phosphonate, any surfactant, any organic acid or any mixture of these. These additives may be used as defoamers, stabilizers, wetting agents, corrosion inhibitors and/or hydrophobic agents.
The metallic surfaces may be contacted with the solution A and/or separately with the solution B by dipping, immersing, roll-coating, squeegeeing or spraying, each application type independent from the other for the solution A resp. B. For coil coating, all kinds of application may be used with the exception of dipping; for other applications all types of application may be used. If in the process of spraying the aqueous solution B considerable amounts of foam should occur, then an adjustment of the spray nozzle concerning the flood effect may be necessary. If spraying is used, it is favorable to minimize the formation of foams, e.g. by selection of an angle of about 45xc2x0; then there will be normally no addition of a defoamer necessary.
The time of contacting the metallic surfaces with the aqueous solution B may be selected from the range of I second to 10 minutes, preferably of 5 seconds to 5 minutes. Therefore, it may be used for coil coating applications having a need of contacting times in the range of from 1 to 30 seconds as well as for other applications where there may be contacting times in the range of from 1 minute to 3 minutes. The process according to the invention may be further varied by applying several coatings to generate a multilayer of organic and inorganic layers by applying e.g. solution B, then solution A, then solution B, then solution A and finally solution B again. The multilayer may have at least 3, preferably 5, favorably up to 12 of these layers. Such multilayers are preferably generated with a zirconium rich solution A. It has been detected that there is an interesting chemical interaction between phosphonic acid functional groups and zirconium which may react again with phosphonic acid functional groups and then with zirconium again, e.g. as zirconyl chloride.
The process according to the invention may be started by subjecting the metallic surfaces to cleaning and/or degreasing before applying the first of the aqueous solutions A resp. B to the metallic surfaces. The cleaning and/or degreasing may be done with the help of conventional alkaline cleaners or solvent cleaners or acidic cleaners or cleaner mixtures. This cleaning and/or degreasing is only necessary if the solution B is the first applied aqueous pretreatment/treatment solution, as the solution A is often as acidic that a cleaning and/or degreasing before applying the solution A is favorable, but not necessary. In both cases, it is preferable to use after cleaning and/or degreasing a deoxidation step which may be carried out by contacting the metallic surfaces with an acidic solution typically with a pH value of up to 3 and which may contain any fluoride. On the other hand, the metallic surface may be cleaned and pickled or only pre-annealed before contacting it with one of the solutions A or B.
If the solution A is the first of the two applied solutions A and B, then there may be a cleaning, rinsing, pickling and one or two times rinsing before applying solution A as may be useful for the pretreatment of wheels. If the solution B is the first of the two applied solutions A and B, then there may be a cleaning and one or two times rinsing before applying solution B as may be useful for the pretreatment of wheels or a cleaning, rinsing, pickling and one or two times rinsing before applying the solution B as may be useful for the pretreatment/treatment of cans or other containers. Preferably, in between any of the process steps and the next following process step of contacting with a reactive liquid there is at least one rinsing with water. In most of the steps, especially after cleaning and/or degreasing, tap water may be used for rinsing, but after the deoxidation as well as after contacting with the solutions A resp. B, de-ionized water is preferred. After the coating with the solution B, there is no necessity to rinse the metallic surfaces, as the unreacted material will not impair paint or other materials adhesion being applied to the coated surfaces later on. The coated metallic surfaces may be dried and/or the excess liquid may be blown away after having been coated with. the solution B. The solution B may therefore be applied in a no rinse method. There should be a rinsing in between contacting the metallic surfaces with the solution A and contacting them with the solution B. This is preferred to avoid drag in of the solution A into the solution B as there may be the risk of reaction of both solutions one with the other, causing precipitation and reducing the concentration of active compounds. In the case that first the solution B is applied and afterwards the solution A, it is preferable to have a rinsing in between because of the same reason, but it is not necessary because of the very small concentration of the effective ingredients of the dragged in liquid into the bath of the solution A. Alternatively, the excess liquid of the solution B could be dried or blown away instead of a rinsing. On the other hand, the drying of excess liquid of the solution A instead of a rinsing may be disadvantageous as there may be a decomposition or damage of the possibly later on applied paint or any other similar layer because of a possible reaction of the residue and the subsequently applied layer.
The metallic surfaces coated with the reaction products and deposited compounds of the solution A resp. B may then be coated with a lacquer, a paint, an adhesive, an after rinse, a sealing, a rubber and/or an organic material, especially with a polymeric material. The rubber layer may be useful for a metal to rubber bonding.
It is preferable that first the solution A is applied and then afterwards the solution B. But it may be favorable, too, first to apply the solution B and then the solution A. In this case, the coating as applied with the solution B may be partially or even only to a very small amount dissolved by applying the solution A. Furtheron, if the afterwards applied coating of the solution A should be thicker, the favorable effect of self assembling molecules will decrease or will be hindered and the advantages of this coating in contact with the later thereon applied layer of a paint or any other polymer containing coating will be reduced. If the coating applied with the solution A should be thin, this favorable effect may be partially or even essentially maintained. If the solution A should show a low or very low concentration, the coating applied by this solution will be quite thin. The combination process according to the invention combines the benefits of two treatments together: The solution A provides coatings which provide excellent corrosion protection by inorganic passivation of the surface. The solution B provides organic coatings, sometimes as monolayers, which create a hydrophobic barrier and also promote excellent paint adhesion. The use of both pretreatments result therefore in complementary protection of the metallic surface. Furtheron, the organic molecules of the compounds of the type XYZ, X*Y*Z* and/or X*Y*Z*Y*X* are reactive especially to zirconium.
The applied coatings are very suitable for applying a lacquer, a paint, an adhesive, an after rinse, a sealing, a rubber and/or an organic material, especially a polymeric material because of excellent adhesive strength, homogeneity of the surface and good reactivity to the functional groups of these further on applied coatings.
The metallic surfaces going to be coated according to the process of the invention may be such of castings, extruded parts, forgings, frames, housings, profiles, sheet stock, small parts, stampings, strips, wheels, wires, parts for aircraft industry, for apparatuses, for automobile industry, for beverage and other containers like cans, for construction or for mechanical engineering.